1. Field of the Invention
The present invention relates to controlling the insertion of sheets into a bundle of stacked sheets with images formed thereon.
2. Description of the Related Art
Some conventional copying apparatuses which are image forming apparatuses have a function of inserting a sheet (hereinafter referred to as “special sheet”) different from a plain sheet to the first page, last page, or middle page of sheets. This function is referred to as a cover mode, an interleaving sheet mode, and so forth according to the page to which the special sheet is inserted. The user sets any of these modes through an operating section provided in such copying apparatuses. For example, a special sheet such as a sheet different in color from a plain sheet, a color copy sheet, or the like can be inserted as a cover sheet, and special sheets can be inserted as dividers between plain sheets every predetermined number of sheets (see U.S. Pat. No. 6,353,726).
Examples of methods to supply special sheets include a method in which special sheets are supplied from a cassette for use in supplying special sheets. Also, there has been proposed a method in which special sheets are supplied from a sheet feeder provided in a sheet processing apparatus such as a finisher which carries out postprocessing on sheets with images formed thereon output from a copying apparatus.
Also, there has been proposed a postprocessing method in which postprocessing such as stapling and punching is carried out on special sheets supplied from the above-mentioned sheet feeder.
In the case where the finisher carries out the above-mentioned postprocessing, a special sheet supplied from the sheet feeder or the cassette is inverted in a predetermined direction and laid over a sheet output from the copying apparatus.
The copying apparatus and the finisher are constructed in consideration of cases where various special sheets (such as a 300 g/m2 sheet which is very thick) are conveyed.
The conventional copying apparatus and finisher, however, have to be large-sized because the curve of an inversion path which inverts special sheets needs to be gentle so as to prevent buckling and jamming of special sheets.
When jamming of a special sheet occurs, the user has to prepare the same special sheet again, which is troublesome for the user and causes cost increase.